Target marker having quantum cascade laser for thermally marking a target

ABSTRACT

A method of marking a target includes intersecting a thermal infrared beam from a handheld housing at room temperature with the target, a portion of a beam path extending from the housing to the target being substantially optically direct. The method also includes viewing the intersected beam with a remote thermal imaging device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.11/464,094, entitled TARGET MARKER HAVING QUANTUM CASCADE LASER FORTHERMALLY MARKING A TARGET, the entire disclosure of which is expresslyincorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A “SEQUENCE LISTING”

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to marking a target, and moreparticularly, to a handheld and/or weapon mounted device incorporating aquantum cascade laser for generating and impinging a thermal infraredbeam upon a target to create a corresponding image in a thermal imager.

2. Description of Related Art

In contrast to image enhancement technology typically employed in “nightvision,” “image intensifier” or “I²” devices, thermal imaging does notrequire any ambient light or supplemental infrared illumination toilluminate a target or to produce an image.

That is, in a thermal imaging device, thermal infrared radiation(typically ranging from approximately 2 microns to 30 microns inwavelength) is captured and converted into a visible image. Objects withtemperatures above 0° Kelvin emit light energy (black body radiation), aportion of which is in the thermal infrared spectrum. Thus, all objectsabove 0° K are theoretically viewable by a thermal imaging device.

In one form of a thermal imaging device (a micro-bolometer array), theinfrared radiation (photons at the infrared wavelength) are impactedagainst a phased array of infrared detector elements, which creates atemperature pattern, often called a thermogram. The thermogram istranslated into electrical impulses which are sent to a signalprocessing unit which translates the information into a display, whereinthe image typically appears as various colors, depending upon theintensity and wavelength of the received infrared emission.

Since certain molecules reacts to specific wavelengths in a predictablemanner, the use of thermal infrared radiation (and sensing of suchradiation) provides a means for identifying or determining the presenceof a selected molecules.

There are several classes of lasers that are capable of emittingradiation in the appropriate wavelength spectrum. However, these devicesrequire cooling to a low temperature.

None of these lasers provide for a handheld, portable configurationoperable at ambient or room temperature. Therefore, the need exists fora handheld portable target marker which can impinge a thermal infraredbeam (at a wavelength between approximately 2 microns and 30 microns)upon the target, thereby identifying the target when viewed with athermal imaging system.

BRIEF SUMMARY OF THE INVENTION

The present target marker provides a portable handheld or weaponsmounted device including firearm-mounted device which can selectivelycreate a beam of thermal infrared radiation having a wavelength which isviewable in a thermal imaging device. The target marker further providesfor operation in a robust configuration at ambient temperatures found infield environments.

In one configuration, the target marker includes a handheld housinghaving an interior and an exterior; a quantum cascade laser retained inthe interior of the housing for emitting a beam at a thermal infraredwavelength along a beam path; a driver retained within the housing andoperably connected to the quantum cascade laser; a collimating orfocusing lens connected relative to the housing and located in the beampath; and a power supply retained within the housing and operablyconnected to the quantum cascade laser.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary of theinvention, and are intended to provide an overview or framework forunderstanding the nature and character of the invention as it isclaimed.

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings are not necessarily to scale,and sizes of various elements may be distorted for clarity. The drawingsillustrate one or more embodiment(s) of the invention, and together withthe description serve to explain the principles and operation of theinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a partial cross sectional view of the target marker.

FIG. 2 is a schematic view of the operable components of the targetmarker.

FIG. 3 is a schematic of the driver circuit of the target marker.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a target marker 10 for use with a thermal imager300 is shown. Although the target marker 10 is shown as a separate andindependent construction from the thermal imager 300, it is contemplatedthe target marker can be cooperatively or integrally connected to thethermal imager. For purposes of description, the target marker 10 is setforth as a separate, remotely deployable device from the thermal imager300.

The thermal imager 300 is known in the art and can be any of a varietyof configurations. The underlying sensing and display technology of thethermal imager 300 is well-developed and employed in devices made byDRS, Raytheon, ITT or BAE. “Thermal imaging” and “thermal detection”refers to imaging and detection in the electromagnetic spectral band of2-30 microns. “Thermal infrared beam” refers to electromagnetic energyin the 2-30 micron wavelength range.

For purposes of disclosure, a brief description of the thermal imager300 is provided. Generally, the thermal imager 300 includes four primarycomponents retained within an imager housing, wherein the imager housingis configured to be carried by an individual.

The first primary component of the thermal imager 300 is a sensor (oftenreferred to as a “camera”) that reacts to infrared radiation, convertingsensed thermal radiation (the “thermal picture”) of an area into avisible thermal image in which, relative to the surrounding environment,hotter areas appear white while cooler areas appear black. One of twosensors is commonly used in portable thermal imagers: (1) a bariumstrontium titanate (“BST”) detector developed by the Raytheon Company ofLexington, MA or (2) a microbolometer with a vanadium oxide (VOx) or anamorphous silicon sensing material, such as the LTC500 MicroIR™ ImagingCamera manufactured and distributed by BAE Systems of Nashua, N.H.

The second primary component the thermal imager 300 is a lens whichfocuses the thermal picture onto the sensor, and specifically onto afocal plane array (“FPA”) of independent pixels. The quality of the lensis an important factor in the quality of the resultant thermal image.One measure of quality is the f-number. A wider lens means a smallerf-number and increased image quality. However, the width of the lens islimited by weight and costs considerations. For this reason, a commonlens provides a field of view up to approximately 60°, and a commonmaterial for lens construction is germanium.

The third primary component the thermal imager 300 is the video display,the means by which the resultant thermal image is provided to the user.An active matrix liquid crystal display (“LCD”) is commonly used inportable thermal imagers.

Finally, the fourth primary component the thermal imager 300 is a powersupply. A NiMH or similar rechargeable battery can be used in portablethermal imagers, although alkaline or other common batteries can be alsoused.

The present target marker 10 can be employed to fulfill any of a varietyof functions. Thus, the term “marker” includes a pointer, an aimer (oraiming device) as well as a designator (target designator). A pointertypically encompasses use of the target marker 10 to identify aparticular location or entity within a group of entities. An aimingdevice is typically used in conjunction with a firearm or crew-servedweapon, wherein the target marker 10 provides an intended point ofimpact of an associated projectile. When used as a designator, thetarget marker 10 is used as or with a target-tracking laser beam and forproviding range data indicative of the range to the target. Each ofthese systems being known in the art, further description is notnecessary.

Thus, “marking” encompasses aiming (aiming from one's own weapon),pointing (indicating for other's weapon system), locating (forconventional and coordinate-guided munitions) and/or designating (forlaser-guided munitions).

The target marker 10 includes a housing 20, a quantum cascade laser 30,a driver 40, a collimating or focusing lens 60 and a power supply 70.

The housing 20 can be a handheld configuration or a firearm mountedconfiguration. The housing is selected to encompass the quantum cascadelaser 30, the focusing lens 60, the driver 40 and the power supply 70.In one configuration, the housing 20 encompasses (retains) all thecomponents required for operation of the quantum cascade laser 30. Thatis, the housing 20 provides the target marker 10 as a self-containedhand-held portable device.

It is contemplated, the housing 20 can include an aperture 21 foremission of a beam from the quantum cascade laser 30. In addition, thehousing 20 can include apertures or ports 23 for control of the targetmarker 10 such as an on/off switch 24, as well as switches or controlsfor operating mode selections.

The housing 20 can be formed of any of a variety of rigid material suchas composites, laminates, plastics or metals. In one configuration, thehousing 20 is formed of an extruded aluminum, thereby providingsufficient strength without requiring significant weight. However, it isunderstood the housing 20 can be machined such as by EDM (electricaldischarge machining) or molding if composites, laminates, plastics oreven metals are employed for the housing.

In one configuration of the target marker 10, the housing 20 isconfigured to mount to any of a variety of handheld, side and small armssuch as pistols, rifles, shotguns, automatic, semi-automatic arms, aswell as bows, collectively referred to as firearms. The housing 20 caninterface with any of a variety of clamping or mounting mechanisms suchas a Weaver style, Picatinny rail or dove tail engagement.

The quantum cascade laser (QCL) 30 is a laser emitting structureretained within the housing 20 and configured via the collimating orfocusing lens 60 made from appropriate materials, to produce a beamextending along a beam path. The beam path extends from the QCL 30,through a portion of the housing 20 to pass to the exterior of thehousing. The QCL 30 is selected to operate in ambient temperatureconditions while producing a beam having a wavelength betweenapproximately 2 μm and 30 μm with a preferred wavelength of 2 to 5 μm or8 to 30 μm.

Although a single quantum cascade laser 30 is shown in housing, it iscontemplated a plurality of quantum cascade lasers can be disposedwithin the housing 20 or a single quantum cascade laser can be employedwith an appropriate driver and filter to provide a plurality ofcorresponding wavelengths.

The QCL 30 includes electrical behavior of a semiconductor materialwhich can be described with the band model, which states that variousenergy ranges, the energy bands, are available to the electrons of thesemiconductor material, and that the electrons of the semiconductormaterial can essentially take on any energy value within the energybands. Various bands can be separated from one another by a band gap,i.e., an energy band with energy values the electrons cannot possess. Ifan electron changes from a higher energy band to a lower energy band,energy corresponding to the difference of the energy values of theelectron before and after the change, which is also called “transition”,is released. The energy difference can be released in form of photons.The band with the highest bound-state energy level, which is fullyfilled with electrons at a temperature of 0° Kelvin, i.e., the so-calledvalence band, and the conduction band that is energetically above thevalence band, which is unfilled at 0° Kelvin, as well as the band gapbetween them are of special significance for a semiconductor material.

In the cascades of quantum cascade lasers, the semiconductor materialsfor the barrier layers and the quantum wells are selected such that thelower conduction band edge of the barrier material lies higher in energythan the lower conduction band edge of the quantum well material. Thelower conduction band edge represents the lowest energy value that anelectron can assume within the conduction band. The energy differencebetween the energy of the lower conduction band edge of the barriermaterial and the lower conduction band edge of the quantum well materialis also called the conduction band discontinuity. As a result of thisselection, the electrons of the quantum wells cannot readily penetratethe barrier layers and are therefore enclosed in the quantum wells. Theelectrons can only “tunnel” through a barrier layer into an adjacentquantum well in a quantum-mechanical process, with the probability ofthe occurrence of a tunneling process depending on the height of theconduction band discontinuity and the thickness of the barrier layerbetween the two quantum wells.

In the quantum well, the behavior of the electrons enclosed in the wellis determined by quantum mechanics effects due to the small thickness ofthe layer (only a few nanometers). An essential effect is that theelectrons in an energy band of the quantum well can no longer assume anyenergy value within the energy range of the band, but rather areconfined to the energy values of specific energy levels, i.e.,sub-bands. The energetic differences between the individual sub-bandsare particularly high if the quantum well is very thin and theconduction band discontinuity is high. The electron energy does notchange continuously, but rather jumps from one sub-band to the next. Theelectron can change from one energy level to the other energy level onlyif the energy increase or the energy decrease suffered by an electroncorresponds precisely to the difference of the energy values of twosub-bands. Transitions from one energy level to another energy levelwithin one and the same band are called intersubband transitions. In thecascades of the quantum cascade laser, the emission of laser radiationoccurs at these intersubband transitions.

QCLs 30 have been constructed to emit laser radiation in a wavelengthspectrum of 3 μm to 100 μm with intersubband transitions in the lasers.J. Faist et al., IEEE journal of Quantum Electronics, Vol. 38, No. 6,July 2002, describes a quantum cascade laser that can emit laserradiation with a wave length of 5.3 μm at room temperature. The cascadesof the quantum cascade laser described in the Faist article are appliedto an InP (indium phosphide) substrate. The quantum wells are comprisedof In_(0.6)Ga_(0.4)As (indium-gallium-arsenide with 60% indium and 40%gallium) and its barrier layers are comprised of In_(0.44)Al_(0.56)As(indium-aluminum-arsenide with 44% indium and 56% gallium).

For emission of wavelengths spectrum of 2.9-5.3 μm at room temperature,the QCL 30 as set forth in US2005/0213627 published Sep. 29, 2005assigned U.S. application Ser. No. 11/061,727 filed Feb. 22, 2005 ishereby expressly incorporated by reference.

In one configuration, the quantum cascade laser 30 is hermeticallysealed within the housing 20, thereby providing a controlled humidityand atmosphere for operation of the laser. Such hermetic sealing caninclude a subhousing or potting of the quantum cascade laser 30. Thesealing can include a sealing of the housing 20, a sealing of the QCL 30as the QCL is retained within the housing, or both.

In a further configuration, the quantum cascade laser 30 can be tuned toprovide a beam of a specific wavelength. Tuning of the beam can beaccomplished by locating a grating in the beam path. The grating can beadjustable to allow selective transmission of a given wavelength, orfixed to transmit only a single wavelength.

The driver 40 can be constructed to provide either pulsed or continuouswave (CW) operation of the QCL 30. The rise/fall time of the pulse,compliance voltage and current for QCL are selected to minimize powerconsumption and heat generation.

The driver 40 is located within the housing 20 and operably connected tothe quantum cascade laser 30. Generally, the driver 40 includes a pulsegenerator, an amplifier and a pulse switcher.

Alternatively, referring to FIG. 3, a schematic of the driver 40operably connected to the QCL 30 is shown. In view of current QCLconstructions, the driver 40 allows for operation as a pulsed laser,such as by passive switching. Although specific values depend upon theparticular QCL and intended operating parameters, it is contemplated thepeak power draw may be between approximately 1 to 10 amps, with anaverage current draw of approximately 0.01 to 0.1 amps. As the requiredvoltage may be from approximately 9 to 12 volts, approximately 9 to 120W may be consumed. This represents a substantial power consumption aswell as heat generation.

A look up table LUT accommodates the temperature induced impedancechanges of the QCL 30. Thus, the look up table LUT can be employed tomodify control of an amplifier in the driver 40 in response to thetemperature of the QCL 30. Depending upon the consistency of the QCL 30(or uniformity of the QCL) in response to temperature changes, the lookup table LUT may be determined for each individual QCL, and hence targetmarker 10, or for a given batch or set of QCLs. As described, oneconfiguration contemplates that the look up table LUT can be burned to aflash memory. Thus, the appropriate compliance voltage to accommodatefor temperature fluctuations of the QCL 30 are carried by the targetmarker 10 in the look up table LUT.

Further, it is contemplated the QCL 30 may be pulsed at frequencies lessthan a millisecond. However, it is understood depending upon theintended use and range of the target marker 10, the repetition rateand/or peak power can be at least factory set as needed. Further, in theconfiguration in which the laser is pulsed, the repetition rate and peakare selected to provide a sufficient beam that can be seen in thethermal imager 300 yet maintain operation of the target marker 10 atambient temperatures. That is, sufficient heat dissipates prior to thenext pulse.

The collimating or focusing lens 60 is disposed in the beam path suchthat in one configuration, the lens is retained within the housing.However, it is contemplated the lens 60 can form an interface betweenthe interior and the exterior of the housing 20. The focusing lens 60can be configured to focus the beam at a particular point. For example,the focusing lens 60 can be configured to focus the beam at a specifieddistance. In a further configuration, the focusing lens can be adedicated collimator, thereby collimating the beam along the beam path.The lens 60 is formed of a material substantially transparent to thewavelength of the beam from the quantum cascade laser 30.

In an alternative configuration, a diffractive optic 80 can be locatedwithin the beam path to provide collimation of the beam. That is, thediffractive optic intersects the beam path such that the beam passesthrough or reflects off of the diffractive optic.

In one configuration, the power supply 70 includes at least one battery.Depending upon the anticipated power requirements, available space andweight restrictions, the batteries can be N-type batteries or AA or AAAbatteries. Additionally, a lithium/manganese dioxide battery such asmilitary battery BA-5390/U, manufactured by Ultralife Batteries Inc. ofNewark, New York can be used with the target marker 10. It is understoodthat any type of power supply 70, preferably portable and sufficientlysmall in size for use in a hand held device can be utilized. The batterytype power supply can be disposable or rechargeable.

The power supply 70 is located within the housing. In one configuration,the housing includes a battery compartment sized to operably retain thebatteries. In the firearm configuration of the target marker 10, thebattery compartment is configured to accommodate any recoil associatedwith any discharge of the firearm. The battery compartment can be formedof a weather resistant, resilient material such as plastic and shaped toinclude receptacles for receiving the battery(ies) required for power.Further, the battery compartment be selectively closeable or sealable toprevent environmental migration into the compartment.

The power supply 70 is operably connected to the driver 40 and can becontrolled by or utilized under driver commands. Thus, the amount ofpower from the power supply 70 can be controlled or varied to alter theoutput of the QCL 30.

In a further configuration, a temperature controller 90 can be disposedin thermal contact with the quantum cascade laser 30 and the exterior ofthe housing 20. The temperature controller 90 is employed to maintainthe quantum cascade laser 30 at a desirable operating temperature. Ascertain configurations of the temperature controller 90 require energyinput, it is advantageous that the housing 20, the quantum cascade laser30 and the driver 40 be configured to minimize thermal demands on thetemperature controller 90. The temperature controller 90 can be apassive device or an active device. A passive temperature controllerincludes heat sinks, radiators or fins to dissipate thermal energy fromthe target marker 10. Active temperature controllers encompass Peltiermodules, Stirling devices as well as fans.

Alternatively, a thermocouple 50 can be thermally coupled to the QCL 30to monitor the temperature, and the electronic look-up table LUT, suchas one encoded in flash memory, can be used to control the driver 40 toachieve the desired optical output.

In a further configuration, the target marker 10 can be used with orincorporate an infrared laser (such as at 830 nm) for use with imageintensifier devices and/or a visible laser (400 nm to 750 nm) such asHL6321 MG manufactured by Hitachi. The visible laser allows for acorresponding designator, pointing or aiming functions which are visiblewithout requiring use of the thermal imager 300.

In a further configuration, the target marker 10 can include a receiverand a transmitter (or a transceiver) for receiving and transmittinginformation from a remote source. Such information can include targetingdata, as well as strategic data, thereby allowing silent coordinatedoperations. As the images of the thermal imager 300 are dynamic, thecommunication with remote sources allows coordination between a remotelocations. The transceiver is operably connected to the power supply. Itis contemplated, the target imager 300, or a central controller caninclude a communicating transceiver with the target marker 10.

In a further configuration, the target marker 10 can be cooperativelyemployed with the thermal imager 300 and a secondary communicationsystem 330. The secondary communication system 330 providescommunication between a user of the target marker 10 and a user of thethermal imager 300 or a separate member in the secondary communicationsystem 330.

The secondary communication system 330 can be a wired system eitherdedicated or open, wherein the signals can be selectively encrypted. Ina further configuration, the secondary communication system 330 caninclude a wireless system operating at any of a variety of frequenciesas well known in the art. Again, the signals over the secondarycommunication system 330 can be selectively encrypted, as known in theart. An exemplary secondary communication system 330 includes, but isnot limited to, third-generation (3G) wireless systems and mobilecommunication services, which can incorporate video teleconferencing andweb browsing. Such 3G systems offer full interoperability (globalroaming) as a result of the international IMT-2000 standardization.Pursuant to radio interface specifications for IMT-2000, five requiredinterfaces enabling interoperability include IMT-DS (Direct Spread),IMT-MC (Multi-Carrier), IMT-TC (Time Code), IMT-SC (Single Carrier), andIMT-FT (Frequency Time). UTRA (W-CDMA) and cdma2000 make up three of thefive IMT-2000 radio interfaces. Both systems utilize code-divisionmultiple access (CDMA) techniques. Alternatively, a Mil-spec compliantsecondary communication system 330 can be employed.

Operation

The target marker 10 is energized by the power supply and a thermalinfrared beam is projected along the beam path. The beam passes throughthe focusing lens and exits the housing. The housing is oriented todirect the beam to impinge or intersect the object of interest, such asa target.

As the beam intersects the target, portions of the beam are scattered orreflected by the surface of the target. A portion of the scattered orreflected beam are captured by the thermal imager 300 and acorresponding visual representation is created. It is also contemplatedthat as the beam intersects the target, a portion of the beam isabsorbed by the target. The absorbed portion of the beam then reemitsenergy within the infrared wavelength which is visible by the targetimager 300.

The target marker 10 is configured to provide an operable range on theorder of a few hundreds of meters. However, as the technology of thethermal imager 300 improves, it is contemplated the target marker 10 canbe modified by increasing the capacity of the quantum cascade laser 30and power supply 70 to provide an operable range on the order ofkilometers.

In those configurations employing multiple wavelengths for providing afused system, the additional wavelengths are captured by correspondingimagers, wherein the corresponding images may be superimposed, blendedor merged to provide a single depiction of the area of interest. Suchsingle depiction can be on the thermal imager 300 or a separate display.

Further, as the thermal imager 300 can have a plurality of targets withan a field of view, the target marker 10 at a remote location can beactivated and directed to intersect the beam with a selected one of theplurality of targets. Communication over the secondary communicationsystem 330 can be employed to supplement the marking of the target bythe remote target marker 10 as viewed on the thermal imager 300.

Although the present invention has been described in terms of particularembodiments, it is not limited to these embodiments. Alternativeembodiments, configurations or modifications which will be encompassedby the invention can be made by those skilled in the embodiments,configurations, modifications or equivalents may be included in thespirit and scope of the invention, as defined by the appended claims

1. A method of marking a target comprising: (a) intersecting a thermalinfrared beam from a handheld housing with the target, wherein thehousing is at substantially ambient temperature, and a portion of a beampath extending from the housing to the target is substantially opticallydirect; and (b) viewing a thermal image of the target and theintersected beam, in the same spectral band, with a thermal imagingdevice.
 2. The method of claim 1, further comprising forming theinfrared beam to have a wavelength between approximately 8 microns and30 microns.
 3. The method of claim 1, further comprising forming theinfrared beam to have a wavelength between approximately 2 microns and 5microns.
 4. The method of claim 1, wherein the housing is hermeticallysealed.
 5. The method of claim 1, wherein the intersected beam formspart of the thermal image of the target.
 6. The method of claim 1,further including collimating the beam.
 7. The method of claim 1,wherein the beam exiting the housing is generated by a single beamemitter.
 8. The method of claim 7, further including activelycontrolling a temperature of the beam emitter.
 9. The method of claim 7,further including passively controlling a temperature of the beamemitter.
 10. The method of claim 1, further including maintaining thehousing at substantially ambient temperature.
 11. A method of marking atarget comprising: intersecting a thermal infrared beam from a quantumcascade laser with the target, wherein the quantum cascade laser isretained in a housing mounted to a firearm, and the housing ismaintained at substantially ambient temperature, the housing containingoptical components disposed within a beam path of the infrared beam, andeach of the optical components being fixed relative to the quantumcascade laser.
 12. The method of claim 11, further comprising formingthe infrared beam to have a wavelength between approximately 8 micronsand 30 microns.
 13. The method of claim 11, further comprising formingthe infrared beam to have a wavelength between approximately 2 micronsand 5 microns.
 14. The method of claim 11, wherein the quantum cascadelaser is hermetically sealed within the housing.
 15. The method of claim11, further including maintaining a substantially uniform temperatureacross the quantum cascade laser.
 16. The method of claim 11, whereinthe intersected beam forms part of a thermal image of the target.
 17. Amethod of marking a target comprising: (a) intersecting a thermalinfrared beam from a housing with the target, wherein the housing ismounted to a firearm, and the housing is maintained at substantiallyambient temperature; (b) controlling the infrared beam to have a fixedwavelength while intersecting the target; and (c) viewing theintersected beam with a thermal imaging device.
 18. The method of claim17, wherein the beam exiting the housing is generated by a single beamemitter.
 19. The method of claim 17, further comprising forming theinfrared beam to have a wavelength between approximately 2 microns andapproximately 30 microns.
 20. The method of claim 17, wherein theintersected beam forms part of a thermal image of the target.
 21. Themethod of claim 1, wherein the infrared beam is formed with a beamsource disposed within the housing, the method further comprisingmodifying control of the beam source in response to a temperature changeprofile corresponding to the beam source.
 22. The method of claim 21,wherein modifying control of the beam source comprises accessing astored compliance voltage corresponding to a sensed temperature of thebeam source.
 23. The method of claim 22, wherein the compliance voltageis included in a look up table, the look up table assisting in modifyingcontrol of an amplifier associated with the beam source.
 24. The methodof claim 23, wherein the amplifier is disposed in a driver operablyconnected to the beam source.
 25. The method of claim 23, wherein thelook up table assists in modifying control of the beam source based ontemperature-induced impedance changes particular to the beam source.